In 1970, Mock in Journal of the American Chemical Society, volume 92, page 7610 disclosed 2,5-di-tert-butyl-thiophene-1,1-dioxide. In 1992, Furukawa et al. in Heterocycles, volume 34, pages 1085-1088, disclosed 2,5-bis(trimethylsilyl)-thiophene-1,1-dioxide. In 1998, Barbarella et al. in Journal of Organic Chemistry, volume 63, page 5497, disclosed 2-(dimethyl-tert-butyl-silyl)-5-bromo-thiophene-1,1-dioxide, 2-n-hexyl-5-bromo-thiophene-1,1-dioxide, 2,5-dibromo-3,4-dihexyl-thiophene-1,1-dioxide and 2,5-di-n-hexyl-thiophene-1,1-dioxide. EP-A 1 041 132 discloses a luminescent organic material for light-emitting devices, characterized by comprising at least one thienyl-S,S-dioxide unit. Specific thiophene-1,1-dioxide compounds are disclosed: 2,5-diphenyl-thiophene-1,1-dioxide, 3,4-dihexyl-2,5-diphenyl-thiophene-1,1-dioxide, 3,4-dineopentyl-2,5-diphenyl-thiophene-1,1-dioxide, 3,4-dimethyl-2,5-diphenyl-thiophene-1,1-dioxide, 3,4-dihexyl-2,5-bis(diphenyl)-thiophene-1,1-dioxide and 2,5-trimethylsilyl-thiophene-1,1-dioxide.
Polythiophenes have been studied extensively due to their interesting electrical and/or optical properties. Polythiophenes become electrically conducting upon chemical or electrochemical oxidation or reduction.
In 1975 Dallacker et al. in Chemische Berichte, volume 108, pages 569-575, disclosed methylenation experiments with 3,4-dihydroxy compounds of diethyl thiophene-, furan-, phenyl-, and 1-(ethoxycarbonylmethyl)-2,5-pyrroledicarboxylate. Methylenations with 3,4-dihydroxy-2,5-thiophenedicarboxylate only led to the 3,4-methylenedioxythiophene derivatives, 3,4-methylenedioxy-2,5-thiophenedicarboxylic acid diethyl ester and 3,4-methylenedioxy-2,5-thiophenedicarboxylic acid diethyl ester-S,S-dioxide respectively, with formation of diethyl dithieno[3,4-b:3′,4′-g]-tetroxecin-1,3,7,9-tetreacarboxylate as a by-product.
EP-A 257 573 discloses an intrinsically electrically conductive polymer, wherein through connection in the 2-position and/or the 5-position are coupled to one another, statistically averaged from 60 to 100% by weight structural units, which are derived from at least one monomer of the formula (1): in which R1 is a C1-C2-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4 and R2 is a hydrogen atom, a C1-12-alkyl group, a C1-12-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4, or R1 and R2 together are —O(CH2)m—CH2— or —O(CH2)m—O— with m=1 to 12, 0 to 40% by weight structural units, which are derived from at least one monomer of the formula (2): wherein R4 and R5 are independently of one another a hydrogen atom, a halogen atom, a C1-12-alkyl group or aryl or together with C-atoms connected to them form an aromatic ring, R3 and R6 independently of one another represent a hydrogen atom or R3 together with R4 and the C-atoms connected to them or R5 together with R6 and the C-atoms connected to them each form an aromatic ring, X represents an oxygen atom, a sulphur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, 0 to 40% by weight structural units, which are derived from at least one monomer of formula (3): where R7, R8, R9 and R10 independently of one another represent a hydrogen atom, a C1-12-alkyl group, a C1-12-alkoxy group or an aryl group, Y and Z independently of one another represent an oxygen atom, a sulphur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, R11 represents an arylene group, a heteroarylene group or a conjugated system of the formula (CH═CH)o, wherein o is 1, 2 or 3, 0 to 40% by weight structural units, which are derived from at least one monomer of formula (4): wherein R12 and R13 independently of one another represent a hydrogen atom, a halogen atom, a C1-12-alkyl group, a C1-12-alkoxy group, a C1-4-alkylamino group or a C1-4-acylamino group, R14 represents a halogen atom, a C1-12-alkyl group, a C1-12-alkoxy group, a C1-4alkylamino group or a C1-4-acylamino group and X has the meaning given above, wherein the polymer in the oxidized form is completely soluble in dipolar aprotic solvents at 25° C. and solutions with a content of at least 0.1 g of the polymer in 100 mL solvent at 25° C. are obtained.
EP-A 339 340 discloses a polythiophene containing structural units of the formula: in which A denotes an optionally substituted C1-4-alkylene group and its preparation by oxidative polymerization of the corresponding thiophene.
EP-A 440 957 discloses dispersions of polythiophenes, constructed from structural units of formula (I): in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together form an optionally substituted C1-4-alkylene residue, in the presence of polyanions.
EP-A-686 662 discloses mixtures of A) neutral polythiophenes with the repeating structural unit of formula (I), in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together represent an optionally substituted C1-4-alkylene residue, preferably an optionally with alkyl group substituted methylene, an optionally with C1-12-alkyl or phenyl group substituted 1,2-ethylene residue or a 1,2-cyclohexene residue, and B) a di- or polyhydroxy- and/or carboxy groups or amide or lactam group containing organic compound; and conductive coatings therefrom which are tempered at elevated temperature, preferably between 100 and 250° C., during preferably 1 to 90 seconds to increase their resistance preferably to <300 ohm/square.
PEDOT/PSS layers have been widely used in light emitting diodes as an intermediate layer between a indium tin dioxide layer and a hole transporting layer. However, the conductivity of such layers is is too high and so-called cross-talk arises resulting in short-circuiting.
There is a need for hole-conducting intermediate layers with a similar work function, but reduced electrical conductivity.